A buried-channel charge-coupled device (CCD) is a solid state transfer device for transferring a charge. Such devices in general include a body of semiconductor material, such as single crystalline silicon, having a channel therein in the form of a region of a conductivity type opposite to that of the semiconductor body, extending along a surface of the body. A plurality of conductive gates extend across and are insulated from the channel and are positioned along the channel. By applying appropriate potentials to the gates in sequence, a charge in the channel can be transferred along the channel. One use for such a CCD transfer device is in an image sensor having a plurality of radiation detectors arranged in columns, and a separate transfer CCD register along each column of detectors with each of the detectors being connected to the CCD. Charges which are generated in the detectors by the radiation received by the detectors are transferred to the connected CCD and then are transferred along the CCD to an output CCD register which extends across the ends of and is connected to the transfer CCD registers and transfers the charges to an output circuit. One such image sensor which uses Schottky-barrier detectors for detecting infra-red radiation is described in the article of W. F. Kosonocky et al., entitled "Design and Performance of 64.times.128 Element PtSi Schottky-barrier Infrared Charge-Coupled Device (IRCCD) Focal Plane Array", published in SPIE, Volume 344, Infrared Sensor Technology (1982), pp. 66-77.
One problem which arises in the use of CCD transfer devices relates to the charge transfer inefficiency of the devices. The charge transfer inefficiency is related to charge transfer losses, which, in a buried-channel CCD, is proportional to the volume of the buried channel. The charge transfer inefficiency of the CCD is of particular concern in an infra-red CCD image sensor which requires low operating temperatures, in the range of 77.degree. to 130.degree. K., since there is a further reduction of charge transfer efficiency at low operating temperatures. This is of particular concern when the image sensor is operating at low single levels which provide signal charges which do not fill the channel of the CCD.